Aeration Characteristics Of Counter-arc Stepped Spillway

High-speed water flow is prone to cavitation damage on the upstream surface of the discharge structure.In order to reduce or eliminate cavitation erosion,many scholars achieved the purpose of aeration erosion reduction by adding aeration facilities or changing the step shape on the traditional right-angle stepped spillway.In this thesis,through numerical simulation,combined with model test and theoretical analysis,the aeration characteristics of a new type of counter-arc stepped spillway are studied.The flow pattern and aeration location of counter-arc stepped spillway under different anti-arc radius and inflow conditions are mainly studied.The main contents and results are as follows:(1)Anti-arc step flow pattern analysis: from the overall flow pattern and local flow pattern,compared to the right-angle step,anti-arc step has a larger cavity height.The discharged water is stored in the anti-arc surface,and a ’ small pool ’ is formed on the antiarc surface.The main stream and the water body on the anti-arc surface shear,collide and a large amount of aeration.The ’ depression ’ of the anti-arc surface intercepts more discharged water flow to participate in the rotary aeration,so that the vortex is more fully developed.The local flow pattern of the anti-arc step is irregular random turbulence.(2)The calculation method of anti-arc step roughness Froude number and step roughness height is proposed: according to the dimensional analysis,combined with the previous research results of aeration characteristics of right-angle step,the calculation method of step roughness height which is suitable for both right-angle step and anti-arc step is proposed,and then the calculation formula of anti-arc step roughness Froude number is given by using the similar calculation form of right-angle step.(3)Analysis of aeration position on anti-arc step surface: Through the observation of model test and numerical simulation,it is found that there is a fluctuation range of aeration position on the surface under the same inflow condition.Through the analysis of the lower and upper limits of the surface aeration position of the six types,the least square method is used to fit the model test and numerical simulation results,and the empirical formula of the lower and upper limits of the surface aeration position when the spillway slope θ=26.6° is obtained.(4)Analysis of the position of aeration at the bottom of the anti-arc step: Under certain inflow conditions,the position of aeration at the bottom is relatively stable.Compared with the right-angle step,the position of aeration at the bottom of the anti-arc step is biased towards the upstream.With the increase of the roughness Froude number,the position of the bottom aeration develops downstream,and the difference between the position of the bottom aeration of the right-angle step and the anti-arc step also increases.According to the results of model test and numerical simulation,under the same roughness Froude number,with the decrease of arc radius,the bottom aeration position is close to the upstream,and the difference of bottom aeration position between different shapes of anti-arc step is very small.The empirical formula of the aeration position at the bottom of the anti-arc step under the spillway slope θ=26.6° is obtained by fitting the data of the aeration position at the bottom of the anti-arc step of six types.